The present invention relates to a soldering material for a spectacle frame produced by soldering metal parts to shape memory alloy parts as well as a spectacle frame produced by using said soldering material.
In recent years, a shape memory alloy has come to be used widely as a material for face-contacting portions of a spectacle frame, such as sides, for comfortably fitting with the user's face and lens-fixing portions such as a rim. A member for connecting such members needs to be provided with drilling, tapping, cutting and other similar machining operations, so that it is necessary to use for such a member a metal which allows such machining operations to be performed readily. In addition, these members need to be soldered, and in the case of a spectacle frame disclosed in Japanese Patent Application No. 67825/1987 filed by the present applicant, a palladium-based soldering material, e.g. silver palladium, is used.
The soldering material based on silver palladium (hereafter referred to as Ag-Pd) used in the above-described application has poor wettability with respect to a shape memory alloy material (hereafter referred to as an SM material) used in face-contacting portions or lens-fixing portions of a spectacle frame, and there has been demand for making improvements on the finishing qualities and productivity.
The wettability referred to here constitutes an important factor in jointing by means of soldering. Generally speaking, an ideal soldering gap is approximately 0.05 mm, and the soldering material fused by heating flows through the gap by means of surface tension and spreads over the entire soldering portion. In this case, if the wettability is poor, the flow between the gap also becomes poor and it is difficult for the soldering material to spread. Consequently, this undesirably results in a lack of jointing strength and the exfoliation of solder.
Soldering materials in general are poor in wettability with respect to SM materials, so that the soldering material extrudes to outside the jointing surface in the form of a lump, which is unsightly. In addition, when such solder is plated, it becomes difficult for the plating to be formed on a member such as a side, a difference in the electric potential occurs between the member and the soldering material, possibly resulting in corrosion due to the battery action. As a result, with such conventional soldering materials, there have been disadvantages in that the strength of the jointed portion subsequently declines and that the deterioration thereof with time is accelerated.